Method and apparatus of using CDD like schemes with UE-RS based open loop beamforming

ABSTRACT

A method and apparatus of wireless communication are disclosed. The wireless communication performs pilot signal transmissions using a first precoding matrix for user equipment specific pilot signals, the pilot signal transmissions having a first transmission rank. The wireless communication also performs data transmissions using a second precoding matrix for data when the data transmissions have a second transmission rank less than the first transmission rank, in which the second precoding matrix includes a transformed version of the first precoding matrix. Alternatively, the wireless communication can perform data transmissions using at least two precoding matrices for data when the data transmissions have a second transmission rank less than or equal to the first transmission rank. Accordingly, the precoding matrix used for data is a transformed version of the precoding matrix used for user equipment specific pilot signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This present application is a continuation of co-pending, commonlyassigned, U.S. patent application Ser. No. 13/253,747, filed Oct. 5,2011, which claims the benefit pursuant to 35 U.S.C. §119(e) of U.S.Provisional Application No. 61/391,016, filed Oct. 7, 2010; and U.S.Provisional Application No. 61/482,164, filed May 3, 2011; whichapplications are specifically incorporated herein, in their entirety, byreference.

BACKGROUND

I. Field

The present disclosure relates generally to wireless communication, andmore specifically to techniques for allocating and using transmissionresources in a multi-input multi-output (MIMO) wireless communicationsystem.

II. Background

Wireless communication systems are widely deployed to provide variouscommunication content such as voice, video, packet data, messaging,broadcast. These wireless systems may be multiple-access systems capableof supporting multiple users by sharing the available system resources.Examples of such multiple-access systems include Code Division MultipleAccess (CDMA) systems, Time Division Multiple Access (TDMA) systems,Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA(OFDMA) systems, and Single-Carrier FDMA (SC-FDMA) systems.

A wireless communication system may include a number of base stationsthat can support communication for a number of user equipments (UEs). Abase station may include multiple transmit and/or receive antennas. EachUE may include multiple transmit and/or receive antennas. In certaindesigns, such as the Release-8 and Release-9 versions of the Long TermEvolution (LTE) standard, a base station may perform pilot and datatransmissions using data transmission techniques such as beamforming,using precoding matrices chosen based on an estimate of the channelbetween the UE and the base station. However, for fast moving UEs, orwhen the channel is rapidly changing, the actual channel during atransmission may be significantly different from the calculated estimateof the channel. It may be desirable to improve the throughput whentransmitting over fast changing channels.

SUMMARY

These and other problems are solved by the disclosed open loopbeamforming techniques using cyclic delay diversity schemes withreference signals, such as user equipment reference signal (UE-RS).

In an exemplary aspect of the present disclosure, a wirelesscommunication method, including performing pilot signal transmissionsusing a precoding matrix for user equipment specific pilot signals, thepilot signal transmissions having a first transmission rank; andperforming data transmissions using at least two precoding matrices fordata, the data transmissions having a second transmission rank less thanor equal to the first transmission rank, in which at least one of the atleast two precoding matrices includes a transformed version of theprecoding matrix for the user equipment specific pilot signals isdisclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including means for performing pilot signaltransmissions using a precoding matrix for user equipment specific pilotsignals, the pilot signal transmissions having a first transmissionrank; and means for performing data transmissions using at least twoprecoding matrices for data, the data transmissions having a secondtransmission rank less than or equal to the first transmission rank, inwhich at least one of the at least two precoding matrices includes atransformed version of the precoding matrix for the user equipmentspecific pilot signals is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including a memory for storing instructions toperform pilot signal transmissions using a precoding matrix for userequipment specific pilot signals, the pilot signal transmissions havinga first transmission rank; and perform data transmissions using at leasttwo precoding matrices for data, the data transmissions having a secondtransmission rank less than or equal to the first transmission rank, inwhich at least one of the at least two precoding matrices includes atransformed version of the precoding matrix for the user equipmentspecific pilot signals; and a processor for executing the instructionsis disclosed.

In another exemplary aspect of the present disclosure, a computerprogram product comprising a tangible computer readable medium storinginstructions, the instructions including code for performing pilotsignal transmissions using a precoding matrix for user equipmentspecific pilot signals, the pilot signal transmissions having a firsttransmission rank; and code for performing data transmissions using atleast two precoding matrices for data, the data transmissions having asecond transmission rank less than or equal to the first transmissionrank, in which at least one of the at least two precoding matricesincludes a transformed version of the precoding matrix for the userequipment specific pilot signals is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication method including performing pilot signal transmissionsusing a first precoding matrix for user equipment specific pilotsignals, the pilot signal transmissions having a first transmissionrank; and performing data transmissions using a second precoding matrixfor data, the data transmissions having a second transmission rank lessthan the first transmission rank, in which the second precoding matrixincludes a transformed version of the first precoding matrix isdisclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus including means for performing pilot signaltransmissions using a first precoding matrix for user equipment specificpilot signals, the pilot signal transmissions having a firsttransmission rank; and means for performing data transmissions using asecond precoding matrix for data, the data transmissions having a secondtransmission rank less than the first transmission rank, in which thesecond precoding matrix includes a transformed version of the firstprecoding matrix is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including a memory for storing instructions toperform pilot signal transmissions using a first precoding matrix foruser equipment specific pilot signals, the pilot signal transmissionshaving a first transmission rank; and perform data transmissions using asecond precoding matrix for data, the data transmissions having a secondtransmission rank less than the first transmission rank, in which thesecond precoding matrix includes a transformed version of the firstprecoding matrix; and a processor for executing the instructions isdisclosed.

In another exemplary aspect of the present disclosure, a computerprogram product comprising a tangible computer readable medium storinginstructions, the instructions including code for performing pilotsignal transmissions using a first precoding matrix for user equipmentspecific pilot signals, the pilot signal transmissions having a firsttransmission rank; and code for performing data transmissions using asecond precoding matrix for data, the data transmissions having a secondtransmission rank less than the first transmission rank, in which thesecond precoding matrix includes a transformed version of the firstprecoding matrix is disclosed.

In another exemplary aspect of the present disclosure, a method ofselectively providing cyclic delay diversity transmissions using userequipment reference signals, the method including determining anoperational state of a channel between a base station and a userequipment; and signaling, based on the determined operational state, atransmission mode to the user equipment wherein at least onetransmission scheme includes user equipment specific pilot transmissionsusing a cyclic delay diversity (CDD) scheme in a resource block using afirst precoding matrix and data transmissions in the resource blockusing one or more of a transformed version of the first precoding matrixis disclosed.

In another exemplary aspect of the present disclosure, an apparatus forselectively providing CDD transmissions using user equipment referencesignals (UE-RS), including means for determining an operational state ofa channel between a base station and a user equipment (UE); and meansfor signaling, based on the determined operational state, a transmissionmode to the user equipment wherein at least one transmission schemeincludes user equipment specific pilot transmissions in a resource blockusing a first precoding matrix and data transmissions in the resourceblock using one or more of a transformed version of the first precodingmatrix is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including a memory for storing instructions todetermine an operational state of a channel between a base station and auser equipment; and signal, based on the determined operational state, atransmission mode to the user equipment wherein at least onetransmission scheme includes user equipment specific pilot transmissionsin a resource block using a first precoding matrix and datatransmissions in the resource block using one or more of a transformedversion of the first precoding matrix; and a processor for executing theinstructions is disclosed.

In another exemplary aspect of the present disclosure, a computerprogram product comprising a tangible computer readable medium storinginstructions, the instructions including code for determining anoperational state of a channel between a base station and a userequipment; and code for signaling, based on the determined operationalstate, a transmission mode to the user equipment wherein at least onetransmission scheme includes user equipment specific pilot transmissionsin a resource block using a first precoding matrix and datatransmissions in the resource block using one or more of a transformedversion of the first precoding matrix.

In another exemplary aspect of the present disclosure, a wirelesscommunication method, including receiving pilot signal transmissionsusing a first precoding matrix for user equipment specific pilotsignals, the pilot signal transmissions having a first transmissionrank; and receiving data transmissions using a second precoding matrixfor data, the data transmissions having a second transmission rank lessthan the first transmission rank, in which the second precoding matrixincludes a transformed version of the first precoding matrix isdisclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including means for receiving pilot signaltransmissions using a first precoding matrix for user equipment specificpilot signals, the pilot signal transmissions having a firsttransmission rank; and means for receiving data transmissions using asecond precoding matrix for data, the data transmissions having a secondtransmission rank less than the first transmission rank, in which thesecond precoding matrix includes a transformed version of the firstprecoding matrix is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including a memory for storing instructions toreceive pilot signal transmissions using a first precoding matrix foruser equipment specific pilot signals, the pilot signal transmissionshaving a first transmission rank; and receive data transmissions using asecond precoding matrix for data, the data transmissions having a secondtransmission rank less than the first transmission rank, in which thesecond precoding matrix includes a transformed version of the firstprecoding matrix; and a processor for executing the instructions isdisclosed.

In another exemplary aspect of the present disclosure, a computerprogram product comprising a tangible computer readable medium storinginstructions, the instructions including code for receiving pilot signaltransmissions using a first precoding matrix for user equipment specificpilot signals, the pilot signal transmissions having a firsttransmission rank; and code for receiving data transmissions using asecond precoding matrix for data, the data transmissions having a secondtransmission rank less than the first transmission rank, in which thesecond precoding matrix includes a transformed version of the firstprecoding matrix is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication method, including receiving pilot signal transmissionsusing a precoding matrix for user equipment specific pilot signals, thepilot signal transmissions having a first transmission rank; andreceiving data transmissions using at least two precoding matrices fordata, the data transmissions having a second transmission rank equal tothe first transmission rank, in which at least one of the at least twoprecoding matrices includes a transformed version of the precodingmatrix for the user equipment specific pilot signals is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including means for receiving pilot signaltransmissions using a precoding matrix for user equipment specific pilotsignals, the pilot signal transmissions having a first transmissionrank; and means for receiving data transmissions using at least twoprecoding matrices for data, the data transmissions having a secondtransmission rank equal to the first transmission rank, in which atleast one of the at least two precoding matrices includes a transformedversion of the precoding matrix for the user equipment specific pilotsignals is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including a memory for storing instructions toreceive pilot signal transmissions using a precoding matrix for userequipment specific pilot signals, the pilot signal transmissions havinga first transmission rank; and receive data transmissions using at leasttwo precoding matrices for data, the data transmissions having a secondtransmission rank equal to the first transmission rank, in which atleast one of the at least two precoding matrices includes a transformedversion of the precoding matrix for the user equipment specific pilotsignals; and a processor for executing the instructions is disclosed.

In another exemplary aspect of the present disclosure, a computerprogram product comprising a tangible computer readable medium storinginstructions, the instructions including code for receiving pilot signaltransmissions using a precoding matrix for user equipment specific pilotsignals, the pilot signal transmissions having a first transmissionrank; and code for receiving data transmissions using at least twoprecoding matrices for data, the data transmissions having a secondtransmission rank equal to the first transmission rank, in which atleast one of the at least two precoding matrices includes a transformedversion of the precoding matrix for the user equipment specific pilotsignals is disclosed.

In another exemplary aspect of the present disclosure, a method ofselectively receiving cyclic delay diversity (CDD) transmissions usinguser equipment reference signals (UE-RS), the method including receivinga transmission mode; and receiving, based on the received transmissionmode, pilot transmissions in a resource block using a precoding matrixand data transmissions in the resource block using a transformed versionof the precoding matrix is disclosed.

In another exemplary aspect of the present disclosure, a n apparatus forselectively receiving cyclic delay diversity (CDD) transmissions usinguser equipment reference signals (UE-RS), including means for receivinga transmission mode; and means for receiving, based on the receivedtransmission mode, pilot transmissions in a resource block using aprecoding matrix and data transmissions in the resource block using atransformed version of the precoding matrix is disclosed.

In another exemplary aspect of the present disclosure, a wirelesscommunication apparatus, including a memory for storing instructions toreceive a transmission mode; and receive, based on the receivedtransmission mode, pilot transmissions in a resource block using aprecoding matrix and data transmissions in the resource block using atransformed version of the precoding matrix; and a processor forexecuting the instructions is disclosed.

In another exemplary aspect of the present disclosure, a computerprogram product comprising a tangible computer-readable memorycomprising instructions for selectively receiving cyclic delay diversity(CDD) transmissions using user equipment reference signals (UE-RS), theinstructions including code for receiving a transmission mode; and codefor receiving, based on the transmission mode, pilot and datatransmissions in a resource block, using a precoding matrix and atransformed version of the precoding matrix, respectively is disclosed.

Various aspects and features of the present disclosure are described infurther detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication system.

FIG. 2 illustrates an exemplary communication system.

FIG. 3 is a flow chart illustrating a base station process of wirelesscommunication.

FIG. 4 is a block diagram representation of a wireless communicationtransmitter apparatus.

FIG. 5 is a flow chart illustrating a base station process of wirelesscommunication.

FIG. 6 is a block diagram representation of a wireless communicationtransmitter apparatus.

FIG. 7 is a flow chart illustrating a user equipment process of wirelesscommunication.

FIG. 8 is a block diagram representation of a wireless communicationreceiver apparatus.

FIG. 9 is a flow chart illustrating a user equipment process of wirelesscommunication.

FIG. 10 is a block diagram representation of a wireless communicationreceiver apparatus.

DETAILED DESCRIPTION

As previously discussed, there is a need to provide a mechanism forimproving transmission performance under fast varying channelconditions. Such a condition may arise, for example, when a userequipment is moving at a high speed with respect to a base station.

In some designs, cyclic delay diversity (CDD) like schemes with userequipment specific reference signals (UE-RS) are used for open loopbeamforming. Pilot and data signals are typically transmitted using thesame precoding matrix. However, in CDD schemes, the pilot signals aretransmitted using a rank greater than or equal to data transmission anddata transmissions are performed by linearly combining one or morevectors of the precoding matrix used for pilots in order to cycle overseveral precoding matrices and make the channel appear ergodic. Theseand other aspects are described in greater detail below.

Briefly and in general terms, certain reference signals, such as theUE-RS, may be used by a base station to perform beamforming fortransmissions from the base station to the UE since the UE can obtainthe precoded channel directly from UE-RS without knowing the precodingmatrix. However, when the channel between a base station and the UE istime varying, the beamforming strategy may suffer if the channelcondition at the time of performing the beamforming is different fromthe channel condition at the time of calculating the direction of thebeam to be used. Therefore, in certain designs, rather than using asingle beam, which may be preferable under certain temporal changes inthe channel, multiple beams may be used for data transmissions. The useof multiple beams may result in greater performance close to the averagecapacity of the channel, as further discussed below.

The techniques described herein may be used for various wirelesscommunication systems such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and othersystems. The terms “system” and “network” are often usedinterchangeably. A CDMA system may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA system may implement a radiotechnology such as Global System for Mobile Communications (GSM). AnOFDMA system may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, or Flash-OFDM®. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA, which employs OFDMA on the downlink and SC-FDMA on theuplink. an organization named “3rd Generation Partnership Project”(3GPP) describes UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM in publisheddocuments. Another organization named “3rd Generation PartnershipProject 2” (3GPP2) describes cdma2000 and UMB in published documents.The techniques described herein may be used for the systems and radiotechnologies mentioned above as well as other systems and radiotechnologies. For clarity, certain aspects of the techniques aredescribed below with respect to LTE (and LTE-A), and LTE terminology maybe used in much of the description below.

FIG. 1 shows a wireless communication system 100, which may be an LTEsystem or some other wireless system. System 100 may include a number ofevolved Node Bs (eNBs) 110 and other network entities. An eNB may be anentity that communicates with the UEs and may also be referred to as abase station, a Node B, or an access point. Each eNB 110 may providecommunication coverage for a particular geographic area and may supportcommunication for the UEs located within the coverage area. To improvecapacity, the overall coverage area of an eNB may be partitioned intomultiple (e.g., three) smaller areas. Each smaller area may be served bya respective eNB subsystem. In 3GPP, the term “cell” can refer to thesmallest coverage area of an eNB 110 and/or an eNB subsystem servingthis coverage area.

UEs 120 may be dispersed throughout the system, and each UE 120 may bestationary or mobile. A UE may also be referred to as a mobile station,a terminal, an access terminal, a subscriber unit, or a station. A UE120 may be a cellular phone, a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, alaptop computer, a cordless phone, a wireless local loop (WLL) station,a smart phone, a tablet, a netbook, or a smartbook.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition a frequency range into multiple(K_(s)) orthogonal subcarriers, which are also commonly referred to astones, bins. Each subcarrier may be modulated with data. In general,modulation symbols are sent in the frequency domain with OFDM and in thetime domain with SC-FDM. The spacing between adjacent subcarriers may befixed, and the total number of subcarriers (K_(s)) may be dependent onthe system bandwidth. For example, K_(s) may be equal to 128, 256, 512,1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 mega-Hertz(MHz), respectively. The system bandwidth may correspond to a subset ofthe K_(s) total subcarriers.

FIG. 2 shows a block diagram of a design of an exemplary basestation/eNB 110 and a UE 120, which may be one of the eNBs and one ofthe UEs in FIG. 1. A UE 120 may be equipped with T antennas 1234 athrough 1234 t, and base station 110 may be equipped with R antennas1252 a through 1252 r, where in general T≧1 and R≧1.

At UE 120, a transmit processor 1220 may receive data from a data source1212 and control information from a controller/processor 1240. Transmitprocessor 1220 may process (e.g., encode, interleave, and symbol map)the data and control information and may provide data symbols andcontrol symbols, respectively. Transmit processor 1220 may also generateone or more demodulation reference signals for multiple non-contiguousclusters based on one or more RS sequences assigned to UE 120 and mayprovide reference symbols. A transmit (TX) multiple-inputmultiple-output (MIMO) processor 1230 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, and/or thereference symbols from transmit processor 1220, if applicable, and mayprovide T output symbol streams to T modulators (MODs) 1232 a through1232 t. Each modulator 1232 may process a respective output symbolstream (e.g., for SC-FDMA, OFDM.) to obtain an output sample stream.Each modulator 1232 may further process (e.g., convert to analog,amplify, filter, and upconvert) the output sample stream to obtain anuplink signal. T uplink signals from modulators 1232 a through 1232 tmay be transmitted via T antennas 1234 a through 1234 t, respectively.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data can typically be a known datapattern that is processed in a known manner and may be used at thereceiver system to estimate the channel response. The multiplexed pilotand coded data for each data stream can then be modulated (i.e., symbolmapped) based on a particular modulation scheme (e.g., BPSK, QSPK,M-PSK, or M-QAM) selected for that data stream to provide modulationsymbols. The data rate, coding, and modulation for each data stream maybe determined by instructions performed by controller/processor 1240.

At base station 110, antennas 1252 a through 1252 r may receive theuplink signals from UE 120 and provide received signals to demodulators(DEMODs) 1254 a through 1254 r, respectively. Each demodulator 1254 maycondition (e.g., filter, amplify, downconvert, and digitize) arespective received signal to obtain received samples. Each demodulator1254 may further process the received samples to obtain receivedsymbols. A channel processor/MIMO detector 1256 may obtain receivedsymbols from all R demodulators 1254 a through 1254 r. Channel processor1256 may derive a channel estimate for a wireless channel from UE 120 tobase station 110 based on the demodulation reference signals receivedfrom UE 120. MIMO detector 1256 may perform MIMO detection/demodulationon the received symbols based on the channel estimate and may providedetected symbols. A receive processor 1258 may process (e.g., symboldemap, deinterleave, and decode) the detected symbols, provide decodeddata to a data sink 1260, and provide decoded control information to acontroller/processor 1280.

On the downlink, at base station 110, data from a data source 1262 andcontrol information from controller/processor 1280 may be processed by atransmit processor 1264, precoded by a TX MIMO processor 1266 ifapplicable, conditioned by modulators 1254 a through 1254 r, andtransmitted to UE 120. At UE 120, the downlink signals from base station110 may be received by antennas 1234, conditioned by demodulators 1232,processed by a channel estimator/MIMO detector 1236, and furtherprocessed by a receive processor 1238 to obtain the data and controlinformation sent to UE 120. Processor 1238 may provide the decoded datato a data sink 1239 and the decoded control information tocontroller/processor 1240.

Controllers/processors 1240 and 1280 may direct the operation at UE 120and base station 110, respectively. Processor 1220, processor 1240,and/or other processors and modules at UE 120 may perform or directprocess 700 in FIG. 7, process 900 in FIG. 9 and/or other processes forthe techniques described herein. Processor 1256, processor 1280, and/orother processors and modules at base station 110 may perform or directprocess 300 in FIG. 3, process 500 in FIG. 5 and/or other processes forthe techniques described herein. Memories 1242 and 1282 may store dataand program codes for UE 120 and base station 110, respectively. Ascheduler 1284 may schedule UEs for downlink and/or uplink transmissionand may provide allocations of resources (e.g., assignment of multiplenon-contiguous clusters, RS sequences for demodulation referencesignals.) for the scheduled UEs.

As stated above, there exits a need to improve performance under fasttime varying channel scenarios. The terms “fast” or “high speed” do notnecessarily imply an absolute value, but are used to denote a relativerate of change in channel condition in relation to the time periodbetween when a channel is estimated and when a transmission is performedusing a precoding matrix selected based on the channel estimate. Forexample, in some designs, a channel that changed from one subframeperiod to the next may be considered “fast time varying.”

In the advanced Long Term Evolution standard for wireless communication(LTE-A), two new types of reference signals were defined. That is, achannel state information-reference signal (CSI-RS) which is used forchannel estimation for feedback purposes and UE-RS which are precodedpilots sent along with data on the data Resource Blocks (RBs). Theprecoding used for the pilots is the same as data.

For low speed UEs 120, the precoders may be selected based on feedbackfrom the UE 120 and may be used before the channel has changedsignificantly. For high speed UEs 120, open loop schemes such asprecoder cycling can be employed where several different (randomlyselected) precoders are used for the data allocated to the UE 120. Asdiscussed above, by “sweeping” the channel in different directions thismay make the channel appear ergodic.

In some designs, a UE-RS based transmission scheme (for both closed loopand open loop beamforming) may involve using the same precoder for bothdata and pilots within an RB (or within a set of contiguous RBs ifbundling is used). In some designs, CDD may be used for data to achievefurther randomization of the precoding vectors. For example, in certaindesigns, in each RB (or each set of bundled RBs if PRB bundling isused), a precoding matrix may be chosen to precode the pilots with.

The chosen precoding matrix P may be of dimension N×r1, where N is thenumber of transmit antennas and r1 is the pilot transmission rank. Rankr1 may be larger than or equal to r, which is a current transmissionrank for data. The pilot transmissions within a set of bundled RBs maybe sent using precoding corresponding to columns of the precoding matrixP. It may be noted that because the pilots are precoded, the UE 120 doesnot need to know the precoding matrix used. However, the UE 120 may needto know the bundling size (number of RBs over which the same precoder isused). Also, the UE 120 may need to know r1 and r. Accordingly, the eNB110 may transmit the transmission ranks r1 and r, used for pilot anddata transmissions, to the UE 120. The UE 120 may also need to know thetransformations that map the precoding matrix P to precoding matricesused for data.

For a data tone, denoted as a function of indices (f,t), where indices fand t denoting the frequency location and time location respectively,the precoding used may be represented as P U(f,t). In thisrepresentation, U(f,t) may be a matrix of dimension r1×r. In certaindesigns, the U matrix may be chosen to utilize full transmission power.In certain designs, U matrix may be chosen such that:U(f,t)*U(f,t)=I, the identity matrix  Eq. (1)

The operation * represents a transpose conjugate (Hermitian adjoint) ofa matrix. In some designs, where r1=r, the U matrix may be a squareunitary matrix (with real or complex entries).

It may be noted that the transformation matrix U is a function ofvariables f and t, implying that a possibly different matrix may bechosen for each data location. In certain designs, the functionaldependence of the entries of the U matrix on the variables f and t maybe chosen a priori and may be known at both the UE 120 and the eNB 110.

In certain designs, when r1=r, one choice of U(f,t) may be:U(f,t)=D(f)U _(R)  Eq. (2)

In Eq. (2), D(f) is a diagonal matrix with elements as shown in Table 1below. In Eq. (2), U_(R) is a fixed unitary matrix depending on thetransmission rank r. It is understood that Table 1 below illustrates oneexample of generating a transformation matrix U and that other examplesmay be implemented as well.

TABLE 1 Num- ber of lay- ers r U_(R) D(f) 2$\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 1 \\1 & e^{{- j}\; 2\;{\pi/2}}\end{bmatrix}$ $\begin{bmatrix}1 & 0 \\0 & e^{{- j}\; 2\;\pi\;{f/2}}\end{bmatrix}\quad$ 3 $\frac{1}{\sqrt{3}}\begin{bmatrix}1 & 1 & 1 \\1 & e^{{- j}\; 2\;{\pi/3}} & e^{{- j}\; 4\;{\pi/3}} \\1 & e^{{- j}\; 4\;{\pi/3}} & e^{{- j}\; 8\;{\pi/3}}\end{bmatrix}$ $\begin{bmatrix}1 & 0 & 0 \\0 & e^{{- j}\; 2\;\pi\;{f/3}} & 0 \\0 & 0 & e^{{- j}\; 4\;\pi\;{f/3}}\end{bmatrix}\quad$ 4 $\frac{1}{2}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & e^{{- j}\; 2\;{\pi/4}} & e^{{- j}\; 4\;{\pi/4}} & e^{{- j}\; 6\;{\pi/4}} \\1 & e^{{- j}\; 4\;{\pi/4}} & e^{{- j}\; 8\;{\pi/4}} & e^{{- j}\; 12\;{\pi/4}} \\1 & e^{{- j}\; 6\;{\pi/4}} & e^{{- j}\; 1\; 2\;{\pi/4}} & e^{{- j}\; 1\; 8\;{\pi/4}}\end{bmatrix}$ $\begin{bmatrix}1 & 0 & 0 & 0 \\0 & e^{{- j}\; 2\;\pi\;{f/4}} & 0 & 0 \\0 & 0 & e^{{- j}\; 4\;\pi\;{f/4}} & 0 \\0 & 0 & 0 & e^{{- j}\; 6\;\pi\;{f/4}}\end{bmatrix}\quad$

FIG. 3 shows a flow chart of a process 300 for wireless communicationimplemented, for example, at the eNB 110. At block 302, pilot signaltransmissions are performed using a first precoding matrix (e.g., thematrix P), the pilot signal transmissions having a first transmissionrank (e.g., r1). At block 304, data transmissions are performed using asecond precoding matrix (e.g., PU(f,t)), the data transmissions having asecond transmission rank (r), less than or equal to the firsttransmission rank is disclosed. The second precoding matrix includes amatrix transformation of the first precoding matrix. Alternatively, datatransmissions can be performed using at least two precoding matriceswhen the second transmission rank is less than or equal to the firsttransmission rank. Accordingly, the precoding matrix used for data is amatrix transformation of the precoding matrix used for user equipmentspecific pilot signals. In some embodiments, the process 300 and theabove-described elements may be varied and are not limited to thefunctions, implementations or examples provided.

FIG. 4 is a block diagram representation of an apparatus 400 forwireless communication. The apparatus 400 includes module 402 forperforming pilot signal transmissions in using a first precoding matrix,the pilot signal transmissions having a first transmission rank andmodule 404 for performing data transmissions using a second precodingmatrix, the data transmissions having a second transmission rank lessthan or equal to the first transmission rank. The second precodingmatrix includes a matrix transformation of the first precoding matrix.Alternatively, data transmissions can be performed using at least twoprecoding matrices when the second transmission rank is less than orequal to the first transmission rank. Accordingly, the precoding matrixused for data is a matrix transformation of the precoding matrix usedfor user equipment specific pilot signals. The apparatus 400 mayimplement the various techniques disclosed herein. In some embodiments,the apparatus 400 and the above-described elements may be varied and arenot limited to the functions, structures, configurations,implementations or examples provided.

FIG. 5 shows a flow chart representation of a process 500 of selectivelyproviding cyclic delay diversity (CDD) transmissions using userequipment reference signals (UE-RS) is disclosed. At block 502, anoperational state of a channel between a base station and a userequipment (UE) is determined. At block 504, a transmission mode issignaled to the (UE) wherein pilot transmissions in a resource block usea precoding matrix and data transmissions in the resource block use oneor more of a transformed version of the precoding matrix. Thetransmission mode signaled may, for example, indicate whether the eNB110 will use the CDD UE-RS-based scheme described above, or willtransmit without using CDD. In some embodiments, the process 500 and theabove-described elements may be varied and are not limited to thefunctions, implementations or examples provided.

FIG. 6 shows a block diagram representation of an apparatus 600selectively providing cyclic delay diversity (CDD) transmissions usinguser equipment reference signals (UE-RS). The apparatus 600 includes amodule 602 for determining an operational state of a channel between abase station and a user equipment (UE) and module 604 for signaling,based on the determined operational state, a transmission mode to the(UE) wherein pilot transmissions in a resource block use a precodingmatrix and data transmissions in the resource block use one or more of atransformed version of the precoding matrix. In some embodiments, theapparatus 600 and the above-described elements may be varied and are notlimited to the functions, structures, configurations, implementations orexamples provided.

FIG. 7 shows a flow chart of a process 700 for wireless communication.At block 702, pilot signal transmissions are received using a firstprecoding matrix, the pilot signal transmissions having a firsttransmission rank. At block 704, data transmissions are received using asecond precoding matrix, the data transmissions having a secondtransmission rank less than or equal to the first transmission rank. Thesecond precoding matrix includes a transformed version of the firstprecoding matrix. Alternatively, data transmissions can be receivedusing at least two precoding matrices when the second transmission rankis equal to the first transmission rank. Accordingly, the precodingmatrix used for data is a matrix transformation of the precoding matrixused for user equipment specific pilot signals. In some embodiments, theprocess 700 and the above-described elements may be varied and are notlimited to the functions, implementations or examples provided.

FIG. 8 is a block diagram representation of a wireless communicationapparatus 800. A module 802 is provided for receiving pilot signaltransmissions using a first precoding matrix, the pilot signaltransmissions having a first transmission rank. A module 804 is providedfor receiving data transmissions using a second precoding matrix, thedata transmissions having a second transmission rank less than or equalto the first transmission rank. The second precoding matrix includes atransformed version of the first precoding matrix. Alternatively, themodule 804 can receive data transmissions using at least two precodingmatrices when the second transmission rank is equal to the firsttransmission rank. Accordingly, the precoding matrix used for data is amatrix transformation of the precoding matrix used for user equipmentspecific pilot signals. In some embodiments, the apparatus 800 and theabove-described elements may be varied and are not limited to thefunctions, structures, configurations, implementations or examplesprovided.

FIG. 9 is a flow chart representation of a process 900 for wirelesscommunication of selectively receiving cyclic delay diversity (CDD)transmissions using user equipment specific reference signals (UE-RS).At block 902, a transmission mode is received. In an aspect, thetransmission mode may include one or more transmission schemes. The oneor more transmission schemes may include the CDD scheme. At block 904,based on the transmission mode, pilot and data transmissions arereceived in a resource block using a precoding matrix and a transformedversion of the precoding matrix, respectively. The precoding matrix mayinclude the matrix P, and the transformed version may include the matrixPU(f,t), as was discussed above.

FIG. 10 is a block diagram representation of an apparatus 1000 forselectively receiving CDD transmissions using UE-RS is disclosed. Theapparatus 1000 includes module 1002 for receiving a transmission modeand module 1004 for receiving, based on the transmission mode, pilot anddata transmissions in a resource block using a precoding matrix and atransformed version of the precoding matrix, respectively. In someembodiments, the apparatus 1000 and the above-described elements may bevaried and are not limited to the functions, structures, configurations,implementations or examples provided.

It will be appreciated that the present disclosure provides techniquesfor transmitting data by using multiple beam formations from the eNB 110to the UE 120. The multiple beam formations may be achieved by using aprecoding matrix for data transmission, which is a transformed versionof a precoding matrix used for pilot transmissions in the same RB. Thetransformation may be performed by multiplying with a matrix.

It will further be appreciated that pilots may be transmitted using atransmission rank higher than the transmission rank used for datatransmission. The rank calculation may be performed using channelquality results obtained from channel state information reference signal(CSI-RS) transmissions or based on uplink measurements.

It will further be appreciated that techniques for using cyclic delaydiversity with UE-RS are disclosed, wherein the same precoder matrix (ora linear combination of vectors thereof) are used for precodingtransmissions. Furthermore, by using matrices that satisfy Eq. (1) tocombine the vectors of the precoder matrix, possible loss oftransmission power level in data transmissions can be mitigated.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, and algorithm steps described in connectionwith the disclosure herein may be implemented as electronic hardware,computer software, or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, circuits, and steps have been describedabove generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Disk and disc, as used herein, includes compact disc (CD),laser disc, optical disc, digital versatile disc (DVD), floppy disk andblu-ray disc where disks usually reproduce data magnetically, whilediscs reproduce data optically with lasers. Combinations of the aboveshould also be included within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of selectively providing cyclic delaydiversity transmissions using user equipment reference signals, themethod comprising: determining an operational state of a channel betweena base station and a user equipment; and signaling, based on thedetermined operational state, a transmission mode to the user equipment,wherein the transmission mode includes at least one transmission schemeincluding: performing user equipment specific pilot transmissions in aresource block using a first precoding matrix; and performing datatransmissions in the resource block using one or more of a transformedversion of the first precoding matrix used for the user equipmentspecific pilot transmissions, wherein the one or more of a transformedversion of the first precoding matrix is obtained by: determining atransformation matrix, wherein values of the transformation matrix aredependent on at least one of frequency and time; and applying thetransformation matrix to the first precoding matrix to obtain the one ormore of a transformed version of the first precoding matrix.
 2. Themethod of claim 1, wherein the determining the operational stateincludes determining a Doppler speed of the user equipment.
 3. Themethod of claim 1, wherein the user equipment specific pilottransmissions have a first transmission rank and the data transmissionshave a second transmission rank.
 4. The method of claim 3, wherein thedata transmissions use at least two precoding matrices when the secondtransmission rank is equal to the first transmission rank.
 5. The methodof claim 1, wherein the user equipment specific pilot transmissions usea first precoding matrix for user equipment specific pilot signals. 6.The method of claim 3, further including determining the firsttransmission rank and the second transmission rank based on userequipment feedback or uplink measurements.
 7. The method of claim 3,further including providing the first transmission rank and the secondtransmission rank to the user equipment.
 8. An apparatus for selectivelyproviding cyclic delay diversity (CDD) transmissions using userequipment reference signals (UE-RS), comprising: means for determiningan operational state of a channel between a base station and a userequipment (UE); and means for signaling, based on the determinedoperational state, a transmission mode to the user equipment, whereinthe transmission mode includes at least one transmission schemeincluding: performing user equipment specific pilot transmissions in aresource block using a first precoding matrix; and performing datatransmissions in the resource block using one or more of a transformedversion of the first precoding matrix used for the user equipmentspecific pilot transmissions, wherein the one or more of a transformedversion of the first precoding matrix is obtained using: means fordetermining a transformation matrix, wherein values of thetransformation matrix are dependent on at least one of frequency andtime; and means for applying the transformation matrix to the firstprecoding matrix to obtain the one or more of a transformed version ofthe first precoding matrix.
 9. The apparatus of claim 8, wherein themeans for determining the operational state includes means fordetermining a Doppler speed of the user equipment.
 10. The apparatus ofclaim 8, wherein the user equipment specific pilot transmissions have afirst transmission rank and the data transmissions have a secondtransmission rank.
 11. The apparatus of claim 10, wherein the datatransmissions use at least two precoding matrices when the secondtransmission rank is equal to the first transmission rank.
 12. Theapparatus of claim 8, wherein the user equipment specific pilottransmissions use a first precoding matrix for user equipment specificpilot signals.
 13. The apparatus of claim 10, further including meansfor determining the first transmission rank and the second transmissionrank based on user equipment feedback or uplink measurements.
 14. Theapparatus of claim 10, further including means for providing the firsttransmission rank and the second transmission rank to the userequipment.
 15. A wireless communication apparatus, comprising: a memoryfor storing instructions to: determine an operational state of a channelbetween a base station and a user equipment; and signal, based on thedetermined operational state, a transmission mode to the user equipment,wherein the transmission mode includes at least one transmission schemeincluding: performing user equipment specific pilot transmissions in aresource block using a first precoding matrix; and performing datatransmissions in the resource block using one or more of a transformedversion of the first precoding matrix used for the user equipmentspecific pilot transmissions, wherein the one or more of a transformedversion of the first precoding matrix is obtained using instructions to:determine a transformation matrix, wherein values of the transformationmatrix are dependent on at least one of frequency and time; and applythe transformation matrix to the first precoding matrix to obtain theone or more of a transformed version of the first precoding matrix; anda processor for executing the instructions.
 16. The apparatus of claim15, wherein the instructions to determine the operational state includeinstructions to determine a Doppler speed of the user equipment.
 17. Theapparatus of claim 15, wherein the user equipment specific pilottransmissions have a first transmission rank and the data transmissionshave a second transmission rank.
 18. The apparatus of claim 17, whereinthe data transmissions use at least two precoding matrices when thesecond transmission rank is equal to the first transmission rank. 19.The apparatus of claim 15, wherein the user equipment specific pilottransmissions use a first precoding matrix for user equipment specificpilot signals.
 20. The apparatus of claim 17, further includinginstructions to determine the first transmission rank and the secondtransmission rank based on user equipment feedback or uplinkmeasurements.
 21. The apparatus of claim 17, further includinginstructions to provide the first transmission rank and the secondtransmission rank to the user equipment.
 22. A non-transitory tangiblecomputer readable medium storing instructions, the instructionscomprising: code for determining an operational state of a channelbetween a base station and a user equipment; and code for signaling,based on the determined operational state, a transmission mode to theuser equipment, wherein the transmission mode includes at least onetransmission scheme including: performing user equipment specific pilottransmissions in a resource block using a first precoding matrix; andperforming data transmissions in the resource block using one or more ofa transformed version of the first precoding matrix used for the userequipment specific pilot transmissions, wherein the one or more of atransformed version of the first precoding matrix is obtained using:code for determining a transformation matrix, wherein values of thetransformation matrix are dependent on at least one of frequency andtime; and code for applying the transformation matrix to the firstprecoding matrix to obtain the one or more of a transformed version ofthe first precoding matrix.
 23. The non-transitory tangible computerreadable medium of claim 22, wherein the code for determining theoperational state includes code for determining a Doppler speed of theuser equipment.
 24. The non-transitory tangible computer readable mediumof claim 22, wherein the user equipment specific pilot transmissionshave a first transmission rank and the data transmissions have a secondtransmission rank.
 25. The non-transitory tangible computer readablemedium of claim 24, wherein the data transmissions use at least twoprecoding matrices when the second transmission rank is equal to thefirst transmission rank.
 26. The non-transitory tangible computerreadable medium of claim 22, wherein the user equipment specific pilottransmissions use a first precoding matrix for user equipment specificpilot signals.
 27. The non-transitory tangible computer readable mediumof claim 24, wherein the instructions further include code fordetermining the first transmission rank and the second transmission rankbased on user equipment feedback or uplink measurements.
 28. Thenon-transitory tangible computer readable medium of claim 24, whereinthe instructions further include code for providing the firsttransmission rank and the second transmission rank to the userequipment.